title: Effects of the prone position on respiratory mechanics and gas exchange during acute lung injury.
abstract: We studied 16 patients with acute lung injury receiving volume-controlled ventilation to assess the relationships between gas exchange and respiratory mechanics before, during, and after 2 h in the prone position. We measured the end-expiratory lung volume (EELV, helium dilution), the total respiratory system (Cst,rs), the lung (Cst,L) and the thoracoabdominal cage (Cst,w) compliances (end-inspiratory occlusion technique and esophageal balloon), the hemodynamics, and gas exchange. In the prone position, PaO2 increased from 103.2 +/- 23.8 to 129.3 +/- 32.9 mm Hg (p < 0.05) without significant changes of Cst,rs and EELV. However, Cst,w decreased from 204.8 +/- 97.4 to 135.9 +/- 52.5 ml/cm H2O (p < 0.01) and the decrease was correlated with the oxygenation increase (r = 0.62, p < 0.05). Furthermore, the greater the baseline supine Cst,w, the greater its decrease in the prone position (r = 0.82, p < 0.01). Consequently, the oxygenation changes in the prone position were predictable from baseline supine Cst,w (r = 0.80, p < 0.01). Returning to the supine position, Cst,rs increased compared with baseline (42.3 +/- 14.4 versus 38.4 +/- 13.7 ml/cm H2O; p < 0.01), mainly because of the lung component (57.5 +/- 25.1 versus 52.4 +/- 23.3 ml/cm H2O; p < 0.01). Thus, (1) baseline Cst,w and its changes may play a role in determining the oxygenation response in the prone position; (2) the prone position improves Cst,rs and Cst,L when the supine position is resumed.
authors.affiliation: Istituto di Anestesia e Rianimazione, Università degli Studi de Milano, Ospedale Maggiore, Istituto di Ricovero e Cura a Carattere Scientifico, Milan, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Pelosi
authors.forename: D
authors.initials: D
authors.lastname: Tubiolo
authors.forename: D
authors.initials: D
authors.lastname: Mascheroni
authors.forename: P
authors.initials: P
authors.lastname: Vicardi
authors.forename: S
authors.initials: S
authors.lastname: Crotti
authors.forename: F
authors.initials: F
authors.lastname: Valenza
authors.forename: L
authors.initials: L
authors.lastname: Gattinoni
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008168:Lung / Q000503:physiopathology; D008171:Lung Diseases / Q000503:physiopathology*; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology; D016684:Prone Position / Q000502:physiology*; D011651:Pulmonary Artery / Q000503:physiopathology; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D015656:Respiratory Mechanics / Q000502:physiology*